MOLECULAR ANALYSIS OF THE P53 GENE IN PANCREATIC ADENOCARCINOMA

Mutations In the p53 tumor suppressor gene are the most common genetic alterations found in human cancer. Most mutations are accompanied by stabilization of the protein, which renders the mutations detectable t hrough immunohistochemical techniques. The immunoreactivity of p53, ho wever, might not cor relate with the result of p53 DNA sequencing. In order to explain the discrepancy, we studied the p53 expressions, muta tions, and changes of the three-dimensional protein structure of mutan t p53 in a series of 61 pancreatic adenocarcinoma specimens using immu nohistochemistry, polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP), DNA sequencing, and computerized protein mod eling. PCR-SSCP followed by DNA sequencing of the p53 gene showed muta tions in 31.2% (19 of 61) of the pancreatic adenocarcinomas. Eight of 19 cases showed p53 immunopositivity. These mutations were located on the surface of the three-dimensional structure or formed unfolded prot eins, which were easily recognized by the antibody. Among other mutati ons in which p53 was immunonegative, five cases with deletions and ins ertion caused frameshift and formation of severely truncated p53 prote in structures unreactive with the antibody used. Ln three cases with p oint mutations, the mutant amino acids were located in the core of the tightly packed beta sandwich inaccessible to the antibody. Three sile nt mutations were immunonegative, corresponding with the absence of am ino acid changes. These results strongly suggest that the analysis of a computer-generated p53 three-dimensional model based on DNA sequenci ng data can assist in evaluating the significance of p53 immunostainin g and mutations fur clinical applications.